城市污泥高含固厌氧消化系统中聚丙烯酰胺的降解及转化机制研究

High-solid anaerobic has been claimed to be advantageous over traditional low-solid anaerobic digestion for several reasons, such as smaller reactor volume and lower energy requirements. However, the addition of polyacrylamide during sludge dewatering results in the risk of soil compaction when the digested sludge is adopted to land utilization. Hence, the key scientific issue confronted by high-solid sludge anaerobic technology is the polyacrylamide degradation mechanism in digestive process. On the basis of verifying the effect of polyacrylamide on the material viscosity and mass transfer in the digestive process, the hydrolysis and degradation process of polyacrylamide is depth studied, the average molecular weight and molecular weight distribution with the digestion time variation is ascertained, and the hydrolysis rate and residual morphology of amide is also investigated. The degradation model of polyacrylamide in the high-solid anaerobic digestion system is culminating established. Furthermore, from biologically speaking, the degradation bacteria which promoting the cleavage of the long carbon chain and the hydrolysis of amide is studied. Then the activity, properties and production conditions of the degradation enzyme secreted by the bacteria are studied to providing the theoretical basis for the further constriction of the engineering bacteria that can efficiently degrade the polyacrylamide.

城市污泥高含固厌氧消化具有设备紧凑、运行节能等优点，但由于在污泥脱水过程中须加入聚丙烯酰胺，其沼渣中残留的聚丙烯酰胺易在最终产物土地利用时导致土壤板结。因此，高含固污泥厌氧消化工艺面临的重要科学问题即为探明聚丙烯酰胺在消化过程中的降解机制。本课题围绕城市污泥的高含固厌氧消化系统，在探明聚丙烯酰胺在消化过程中的对物料粘度、基质传质的影响的基础上，深入研究系统中聚丙烯酰胺的水解与降解过程，探明其平均分子量及其分子量概率分布随着消化时间的变化规律，考察其酰胺基的水解率及其水解后的残留形态，最终建立聚丙烯酰胺在城市污泥高含固厌氧消化系统中的降解模型。并研究脱水污泥中促进聚丙烯酰胺长碳链的裂解和酰胺基的水解转化的降解菌种，针对该菌种分泌的降解酶的酶活性、酶学性质和产酶条件进行研究，进一步为构建针对厌氧消化系统的高效降解聚丙烯酰胺工程菌提供理论依据。

城市污泥高含固厌氧消化具有设备紧凑、运行节能等优点，但由于在污泥脱水过程中须加入聚丙烯酰胺，其沼渣中残留的聚丙烯酰胺易在最终产物土地利用时导致土壤板结。因此，高含固污泥厌氧消化工艺面临的重要科学问题即为探明聚丙烯酰胺在消化过程中的降解机制。本课题围绕城市污泥的高含固厌氧消化系统，探明脱水污泥中PAM作为氮源和碳源经厌氧消化后被生物降解的机理，并量化其降解产物形态及含量。研究结果发现，PAM作为碳源的利用率不受PAM初始浓度的影响，但PAM作为氮源时，其利用效率受到其产物氨氮的影响；PAM在厌氧消化初期长碳链的降解产物主要以两到三个碳原子的短链有机物为主，随着PAM的降解，分子量不断变小，其长碳链的长度也不断减小，PAM的生物抗性逐渐降低，开始大量断裂产生3个碳原子以上的短链酸，同时其支链上的酰胺基水解为羧基和氨氮，相邻的羧基进一步反应形成醚基；PAM经厌氧消化后支链水解效率较低，致使未水解的PAM降解后会产生有毒单体丙烯酰胺。为了解决这个问题，对厌氧消化系统从关键酶活性[水解酶(酰胺酶)和解聚酶(乙醇脱氢酶)以及主要的酸化酶(磷酸转丁酰酶、丁酸激酶、磷酸转乙酰酶、乙酸激酶、草酰乙酸转羧化酶和琥珀酰辅酶A转移酶)]、污泥絮体颗粒尺寸等理化特性和微生物菌群分布特性[主要降解菌Proteobacteria菌种相对丰度]等方面综合考虑进行优化，优化后的系统可同时提高产甲烷性能和PAM水解效率，从而减少了有毒单体丙烯酰胺的累积。由回归模型预测结果可知：最佳工艺参数初始pH值为9.0，PAM浓度为200 mg/L，消化时间为17d时，在此条件下，PAM水解率可达85%。